(a) Field of the Invention
The present invention relates to a wound rotor driving motor and more particularly, to a rotor cooling structure of a wound rotor driving motor that cools a rotor coil with external air as an open structure of a non-molding method.
(b) Description of the Related Art
In general, a hybrid electric vehicle or an electric vehicle generates driving torque using an electric motor (hereinafter referred to as a “drive motor”) that develops torque with electrical energy. For example, a hybrid electric vehicle may be driven in an electric vehicle (EV) mode, which is a pure electric vehicle mode where power of a drive motor is used, or in a hybrid electric vehicle (HEV) mode, where torques of an engine and a drive motor are simultaneously used as power. In other words, a general electric vehicle drives using a torque of a drive motor as power.
Typically, drive motors used as power sources of environmentally-friendly vehicles are permanent magnet synchronous motors (PMSMs). For example, PMSMs must maximize performance of permanent magnets to exhibit maximum performance in a restricted layout condition. In the permanent magnet, a neodymium (Nd) component enhances intensity of a permanent magnet, and a dysprosium (Dy) component enhances high temperature demagnetization tolerance. However, a rare earth (Nd, Dy) metal component of such a permanent magnet is limitedly buried, is very expensive, and may have severe price fluctuations. Accordingly, application of an induction motor has recently been considered, however, to exhibit the same motor performance, an excessive size increase in the volume and the weight thereof, is required.
Currently, development is occurring of a Wound Rotor Synchronous Motor (WRSM) to replace a Permanent Magnet Synchronous Motor (PMSM) as a drive motor used as a power source of an environmentally-friendly vehicle. By forming a rotor in an electromagnet when applying a current by winding a coil in a rotor and a stator, a WRSM replaces a permanent magnet of a PMSM. In such a WRSM, the rotor is disposed at a predetermined air gap within the stator. When power is applied to a coil of the stator and the rotor, a magnetic field is formed, and the rotor rotates by a magnetic action occurring therebetween. Unlike a PMSM, the WRSM winds a coil to a rotor when the rotor rotates at a high speed (e.g., in a normal EV, about 10,000 rpm or greater), a rotor coil may be separated by centrifugal force. To prevent such an occurrence, in the related art, an end coil cover is mounted within opposing end portions of a rotor, and by molding a resin within the end coil cover, a rotor coil is fixed.
Further, a WRSM has a structure in which a rotor is disposed at a predetermined air gap within a stator and may generate a magnetic flux by applying a current to a rotor coil through a brush and a slip ring. Accordingly, in a WRSM, copper loss occurs by resistance of a rotor coil, and which causes performance of a motor to deteriorate by causing heating of the rotor coil.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.